linux-kernel - Re: [PATCH 2/2] mm/thp: Rename pmd_mknotpresent() as pmd

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Date:   Mon, 20 Apr 2020 22:03:55 +0100
From:   Will Deacon <will@...nel.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-mm@...ck.org, Vineet Gupta <vgupta@...opsys.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        nouveau@...ts.freedesktop.org, linux-snps-arc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm/thp: Rename pmd_mknotpresent() as pmd_mknotvalid()

On Fri, Mar 20, 2020 at 10:24:17AM +0530, Anshuman Khandual wrote:
> pmd_present() is expected to test positive after pmdp_mknotpresent() as the
> PMD entry still points to a valid huge page in memory. pmdp_mknotpresent()
> implies that given PMD entry is just invalidated from MMU perspective while
> still holding on to pmd_page() referred valid huge page thus also clearing
> pmd_present() test. This creates the following situation which is counter
> intuitive.
> 
> [pmd_present(pmd_mknotpresent(pmd)) = true]
> 
> This renames pmd_mknotpresent() as pmd_mknotvalid() reflecting the helper's
> functionality more accurately while changing the above mentioned situation
> as follows. This does not create any functional change.
> 
> [pmd_present(pmd_mknotvalid(pmd)) = true]
> 
> This is not applicable for platforms that define own pmdp_invalidate() via
> __HAVE_ARCH_PMDP_INVALIDATE. Suggestion for renaming came during a previous
> discussion here.

Bikeshed alert: maybe pmd_mkinvalid() would be better, given that this is
a one-trick pony for pmdp_invalidate()?

Will